Molecular structure of SiOx-incorporated diamond-like carbon films; evidence for phase segregation

Silicon-oxide incorporated amorphous hydrogenated diamond-like carbon films (SiOx–DLC, 1 ≤ x ≤ 1.5) containing up to 24 at.% of Si (H is excluded from the atomic percentage calculations reported here) were prepared using pulsed direct current plasma-enhanced chemical vapour deposition (DC-PECVD). Molecular structure, optical properties and mechanical properties of these films were assessed as a function of Si concentration. The spectroscopic results indicated two structural regimes. First, for Si contents up to ~ 13 at.%, SiOx–DLC is formed as a single phase with siloxane, O–Si–C2, bonding networks. Second, for films with Si concentrations greater than 13 at.%, SiOx–DLC with siloxane bonding and SiOx deposit simultaneously as segregated phases. The variations in mechanical properties and optical properties as a function of Si content are consistent with the above changes in the film composition.